What is the pacemaker of the heart?

Cells in the SAN

What do cells in the SAN do?

What happens in the pacemaker potential?

There is turning on of a slow Na conductance, called the funny current. Opening of Ca channels

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What sets the rhythm of the heart?

AP firing in the SA node

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What effect does sympathetic activity have on the pacemaker potential?

It increases the slope of the pacemaker potential

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What is the effect of the SNS on the pacemaker potential mediated by?

ß1 receptors that are G-protein coupled receptors

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How do ß1 receptors mediate the effect of the SNS on the pacemaker potential?

They increase cAMP production by stimulating adenyl cyclase.

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What effect does parasympathetic activity have on the pacemaker potential?

In decrease the slope

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What is the effect of the PNS on the pacemaker potential mediated by?

M2 receptors, which are G protein-coupled receptors

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How do M2 receptors mediate their effect on the pacemaker potential?

They increase K conductance, and decrease cAMP by inhibiting adenyl cyclase. K brings the membrane potential down, further from threshold

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What effect does noradrenaline have on the force of contraction?

It increases it

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How does noradrenaline exert its effect on the force of contraction?

It acts on ß1 receptors in the myocardium, which causes an increase in cAMP, activating protein kinase A

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How does the activation of PKA lead to an increased force of contraction?

Phosphorylation of Ca channels open them, increasing Ca entry during the plateau of the AP. This leads to an increased uptake of Ca into the SR Leads to increased sensitivity of contractile machinery to Ca

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How does increased uptake of Ca into the SR increase the force of contraction?

It increases build up, so there is more Ca to be released Increased uptake reduced duration of contraction, which is necessary if need the heart to fire at a faster rate

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What do most vessels receive?

Sympathetic innervation

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What vessels do not receive sympathetic innervation?

Apart from some specialised tissue, such as erectile tissue, which receives parasympathetic tissue

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What receptors do most arteries and veins have?

α1 adrenoreceptors

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What vessels also have ß2 receptors?

Coronary, liver and skeletal muscle vasculature

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How does the affinity of circulating adrenaline differ between α1 and ß2 receptors?

It has a higher affinity for ß2 receptors

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What does adrenaline do at physiological concentrations?

Preferentially bind to ß2 adrenoreceptors

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What will adrenaline do at higher concentrations?

Activate α1 receptors

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What does vasomotor tone allow for?

Vasodilation to occur

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What leads to vasodilation?

Decreased sympathetic output

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What leads to vasomotor tone?

Normal sympathetic output

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What leads to vasoconstriction?

Increased sympathetic output

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What effect does activating ß2 receptors have on vessels?

It causes vasodilation

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How does activation of ß2 receptors lead to vasodilation?

Causes an increase in cAMP, which activates PKA. This opens K channels, and inhibits MLCK, leading to relaxation of smooth muscele